Magnetic drive pumps have been employed which eliminate the need for the drive shaft to pass through the exterior of the pump enclosure to the pump chamber. In a magnetic drive pump, two shafts including a drive shaft and a rotor shaft, are utilized as opposed to a single drive shaft.
An example of a conventional magnetic drive pump 20 is illustrated in FIG. 1. A drive shaft 21 passes through a barring carrier assembly 22 which is connected to coupling bracket 23 which, in turn, is connected to the casing 24. The proximal end 25 of the drive shaft 21 is coupled to the motor or driver (not shown) often by a keyed or key-type coupling. A slot or groove in the proximal end 25 of the drive shaft 21 is shown at 26 for this purpose. The drive shaft passes through a bearing assembly 27 which provides bearing support for the shaft 21. The distal end 30 of the drive shaft is connected to an outer magnet assembly 28 which includes a proximal end 29 that is fixed to the drive shaft 21 by one or more fasteners, such as the set screw shown at 31. A distal cylindrical section 32 of the outer magnet assembly 28 forms a cup that extends axially beyond the distal end 30 of the drive shaft 21 and includes an. inner surface 33 that is connected to a plurality of outer magnets 34.
The outer magnet assembly 28 surrounds an inner magnet assembly 35. The inner magnet assembly 35 includes an annular sleeve 36 that is connected to a rotor shaft 37, often by a key-type connection illustrated by the groove 38 disposed towards the proximal end 39 of the rotor shaft 37 and the key 40 disposed on the inner cylindrical wall of the sleeve 36 of the inner magnet assembly 35. The annular sleeve 36 is connected to a plurality of inner magnets 41 disposed between and connected to potting compound shown at 42. The inner magnet assembly 35 also includes a cover 43 and the entire assembly is disposed within a canister 44 (or “can”) that is connected to the coupling bracket 23 and casing 24 by way of the annular flange 45 being sandwiched between the casing 24 and coupling bracket 23 which, as noted above, are connected together.
In the conventional design shown in FIG. 1, the proximal end 39 of the rotor shaft 37 is connected to a spacer or washer 46 which is also disposed within the sleeve 36 of the inner magnet assembly 35. No bearing support is provided for the proximal end 39 of the rotor shaft 37. Instead, the rotor shaft 37 passes through one or more bushings 47 disposed between the proximal end 39 and the distal end 48 of the rotor shaft 37.
The distal end 48 of the rotor shaft then is conventionally connected to a rotor 49 which is enmeshed with an idler 51 that is connected to an idler shaft or pin 52 which, in turn, is connected to the head 53. The head 53 in combination with the casing 24 defines a pump chamber in which the rotor 49 and idler 51 are disposed. A crescent 54 is connected to the head 53.
In designs similar to that shown in FIG. 1, the axial position of the rotor shaft 37 within the casing 24 may be less stable than desired resulting in the possibility of axial forces being imposed on the rotor 49 and idler 51, in the pump chamber. Further, the lack of bearing support at either the proximal end 39 or the distal end 48 of the rotor shaft 37 may be problematic in some designs resulting in the proximal end 39 and the distal end 48 of the shaft 37 being exposed to excessive frictional forces thereby requiring more frequent maintenance.
Still another problem associated with the design shown in FIG. 1 is the use of the pumped fluid as a coolant for the components disposed within the canister 44. Specifically, input or output ports of the pump chamber are shown in phantom at 55. The rotor shaft 37 is hollow and includes an axial passageway shown in phantom at 56. In addition to being pumped between the input and output ports 55, fluid also migrates from the pump chamber, through the distal end 49 or the rotor shaft 37 and down the axial passageway 56 of the rotor shaft 37 to the canister 44 thereby providing fluid to the canister 44 which serves as a coolant. Further, if the fluid being pumped is extremely abrasive, such as a metal particulate slurry, damage to the inner magnet assembly 35 may occur as the canister 44 or cover 43 may receive undue wear from the abrasive liquid. Finally, some liquids are not suitable for use as a coolant medium for the inner magnet assembly 35. Specifically, if the liquid being pumped is at a elevated temperature and is subject to a liquid-to-solid phase change at a lower temperature, such a liquid would not be suitable as a coolant for the inner magnet assembly 35 because it may be prone to a liquid-to-solid phase change within the inner magnet assembly 35 which, of course, would inhibit or block flow through the inner magnet assembly 35 and require more frequent maintenance.
Thus, there is a need for an improved design which provides improved bearing support and axial stability for the rotor shaft 37. Also, there is a need for an improved system for cooling the components contained within the canister 44 which include the inner magnet assembly 35 and proximal end 39 of the rotor shaft 37.